When Blender says out of memory error what exactly do I need to free up or replace?
Are you rendering it on GPU or CPU?
If it's GPU then you 

(a) try splitting up and rendering the scene over different render layers

-OR-

(b) try rendering it on CPU instead. I had to render a complex scene too earlier this month, it kept crashing every time I tried to rendering it on GPU; worked just fine on CPU however it took longer (obviously). If the problem still persists on CPU rendering then you could consider upgrading your RAM; I, myself, have 16GB and that just barely enough for complex renders.